Drilling rigs may include alternating current (“AC”) 3-phase induction motors. The speed of the motors may be controlled using variable frequency drives (“VFDs”). Each VFD may include one or more inverters, and the inverters may generate AC current having a controlled frequency due to pulse-width modulation (“PWM”) of one or more insulated-gate bipolar transistors (“IGBTs”) in the VFD. The current transmitted from the VFDs to the motors generates noise. More particularly, when the inverters in the VFDs are not synchronized, the switching of the IGBTs in different VFDs is not in phase, which generates the noise. The noise may also be due to harmonics generated by switching the IGBTs of the VFD inverter or diodes/thyristors of the VFD rectifier, resonances generated by switching the IGBTs or thyristors, or a combination thereof. The noise may also be due to intermodulation between multiple signals of similar frequency content, or the interaction of multiple drives on the same input direct current (“DC”) power filter.
The noise may interfere with measurements performed at the surface. For example, the noise may interfere with sensing electromagnetic (“EM”) telemetry signals that are transmitted to the surface from a downhole tool in a wellbore.